Дисертації з теми "Contact crack"
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Hannes, Dave. "Growth of cracks at rolling contact fatigue." Thesis, KTH, Hållfasthetslära (Avd.), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33659.
Повний текст джерелаUtmattning med rullande kontakter är ett ofta förekommande problem för många maskinelement. I den aktuella rapporten utfördes en numerisk studieför att förutsäga sprickvägen hos utmattningssprickor som initierats i ytan vidrullande kontakter. Implementeringen av kontaktproblemet bygger på asperitpunktlastmekanismen för rullande kontakter. Studien av kontaktproblemetär tillämpad till kugghjul. Olika belastningstyper och modeller studeradesoch jämfördes med profilen hos en experimentell spall. Bra överensstämmelseobserverades för korta spricklängder när en modell med fördelad belastninganvänds för en belastningstyp där en normalbelastning agerar på asperiten ochvid cylindriska kontakten och en tangentialbelastning införs på asperiten. Olikakriterier för spricktillväxt implementerades för att verifiera giltigheten av antagandetatt mode I spricktillväxt är dominant. Några generella kännetecken avutmattningssprickor med rullande kontakter framhävdes. En kvantitativ parameterstudie för den implementerade modellen utfördes.
Dharmarajan, Vignesh. "An Investigation on Spur Gear Rolling Contact Fatigue Crack Initiation and Crack Propagation under EHL Condition." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1578319670376195.
Повний текст джерелаKapoor, A. "Geometry changes and crack initiation in rolling and sliding contact." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234987.
Повний текст джерелаWilliams, Tracy Denise. "Remote condition monitoring of rolling element bearings with natural crack development." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17243.
Повний текст джерелаAlfredsson, Bo. "A study on contact fatigue mechanisms." Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3028.
Повний текст джерелаWidiyarta, I. M. ade. "Simulation of wear and crack initiation in line contact with thermal stresses." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512030.
Повний текст джерела田中, 啓介, Keisuke TANAKA, 義明 秋庭, Yoshiaki AKINIWA, 拓也 加藤, Takuya KATO, 弘樹 高橋 та Hiroki TAKAHASHI. "繰返しねじり・引張複合荷重下での予き裂からの疲労き裂進展経路の予測". 日本機械学会, 2005. http://hdl.handle.net/2237/9131.
Повний текст джерелаHannes, Dave. "Modelling of surface initiated rolling contact fatigue crack growth using the asperity point load mechanism." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-34005.
Повний текст джерелаMouginot, Rémi. "Fractures d'indentation elastique." Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0087.
Повний текст джерелаRuellan, Du Créhu Arnaud. "Tribological analysis of White Etching Crack (WEC) failures in rolling element bearings." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0116.
Повний текст джерелаDespite constant expansion and engineering progress, wind turbines still present unexpected failures of heavy duty mechanical components drastically affecting the cost of energy. Among the most prevalent tribological failures in wind turbine rolling element bearings, a peculiar rolling contact fatigue mode has been associated to broad subsurface three-dimensional branching crack networks bordered by white etching microstructure, and thus named White Etching Cracks (WEC). Compared to conventional microstructural alterations, WECs tend to develop at moderate loads and cycles eventually leading to premature failures that remain unpredictable using fatigue life estimations. Far from being generic to specific manufacturers, WECs occur in various industrial applications, for various bearing types, components, lubricants, steels grades and heat treatments. As WEC occurrences present no common evident denominator, they remain delicate to reproduce on laboratory test rigs without prior artificial hydrogen charging, so that no consensus on WEC formation mechanisms have been confirmed yet. In this study, a thorough tribological analysis of WEC formation mechanisms has been led. Expertise protocols have been established to best reveal and observe WECs that commonly develop at unconventional locations versus the contact area. First analysis of WEC reproductions on standard rolling element bearings either hydrogen precharged or kept neutral have signified that artificial hydrogen charging, commonly employed to apprehend the failure mode, results in similar WEC morphologies but tends to alter WEC tribological initiation. In consequence, WEC reproductions in remarkably different configurations but without hydrogen charging have been compared in order to propose a better understanding of WEC surface-affected formation mechanisms: first, initiation via tribochemical hydrogen permeation at nascent steel surfaces formed either directly at the raceway or at surface microcracks flanks and second, propagation by local hydrogen embrittlement at crack tips function of the stress state. An extensive root cause analysis have then been led suggesting that WEC may be associated to various combinations of macroscopic operating conditions that often interact and come down to similar tribological parameters including high sliding energy thresholds, specific lubricant formulations and tribochemical drivers such as water contamination and/or electrical potentials. Further investigations on a minimalist twin-disc fatigue tribometer have provided additional evidence that WEC influent drivers are non-self-sufficient, supporting that WEC formation mechanisms rely on a subtle equilibrium between tribo-material, tribo-mechanical and tribo-chemical drivers that all should be mastered to design efficient and durable countermeasures
Hannes, Dave. "On fatigue crack growth modelling of surface initiated rolling contact fatigue using the asperity point load mechanism." Doctoral thesis, KTH, Hållfasthetslära (Avd.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141151.
Повний текст джерелаQC 20140210
Udthala, Aparna. "Contact Fatigue of Spur Gear Operating Under Starved Lubrication Condition." Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1619554628009744.
Повний текст джерелаSun, Ta-chien. "Fundamental study of contact resistance behavior in RSW aluminum." Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1069807481.
Повний текст джерелаTitle from first page of PDF file. Document formatted into pages; contains xxviii, 314 p.; also includes graphics (some col.) Includes bibliographical references (p. 303-314). Available online via OhioLINK's ETD Center
Noyel, Jean-Philippe. "Analyse de l’initiation de fissures en fatigue de contact : Approche mésoscopique." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0126/document.
Повний текст джерелаContact fatigue is the predominant mode of failure of components subjected to a repeated contact pressure, like rolling element bearings or gears. This phenomenon is known as rolling contact fatigue (RCF). A large number of models have been developed to predict RCF, but there is today no complete predictive life model, and understanding RCF failure mechanism remains a significant challenge. RCF failure mechanisms are known to be very sensitive to a large number of parameters linked to contact conditions (roughness, lubrication) or materials (inclusions, gradients properties, residual stresses…). To improve knowledge about the influence of these parameters on failure mechanisms and life, a numerical model is developed to simulate the progressive damage of a component subject to rolling contact fatigue. Mechanisms associated with the initiation stage of failure process are located at a scale lower than the macroscopic scale. The proposed approach is to develop a grain level model (mesoscopic scale) in order to focus on initiation mechanisms. A Voronoi tessellation is used to represent the material microstructure. The progressive deterioration is simulated by applying the concept of damage mechanics at grain boundaries represented by cohesive elements. This approach has been first applied to a 2D isotropic model. The numerical behaviour of cohesive elements has been investigated: the influence of cohesive stiffness has been analysed and singularities at the triple junctions has been highlighted. The representativeness of the original model was improved by modelling crystal anisotropy. A cubic elasticity model was used to represent the behaviour of grains. Finally, a thorough analysis of the application of the damage concept at grain boundaries highlighted that the initial formulation results in a very low influence of the damage on the intergranular shear stress. A new formulation leading to a direct influence of the damage on the intergranular shear stress has been proposed. This new formulation has resulted in (i) a change in the distribution of micro-cracks, with coalescence between the different micro-cracks, and (ii) a large increase in the RCF life estimated by the model. The order of magnitude of the number of cycles corresponding to the first micro-cracks is comparable to that given by experiments
Emami, Anahita. "Investigation on Physics-based Multi-scale Modeling of Contact, Friction, and Wear in Viscoelastic Materials with Application in Rubber Compounds." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/97008.
Повний текст джерелаPHD
Azeggagh, Nacer. "Damage mechanisms in silicon nitride materials under contact loading." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0075/document.
Повний текст джерелаThis work deals with the mechanical properties and damage mechanisms under contact loading of dense and porous silicon nitrides materials. These technical ceramics exhibit a very interesting combination of mechanical properties: low density, high hardness and strength, good corrosion resistance and a low thermal coefficient. They are used in many applications including ball bearings for the automotive and aerospace industries. The characterization of the local behaviour under contact loading is then a crucial issue. Spark plasma sintering technique is used to process silicon nitride ceramics with addition of different amount of yttrium oxide as sintering aid. Controlling the sintering temperature and the applied pressure has permitted to obtain materials with fine, medium and coarse microstructures. In addition, materials with different porosity contents have been obtained. First, we have investigated the influence of processing conditions (temperature, pressure, amount of yttria on the microstructure and mechanical properties at the macroscopic scale (elastic parameters, Vickers hardness, flexural resistance ...). Hertzian contact tests were then performed to identify the damage mechanisms at the surface and subsurface of the sintered materials. The use of indenting spheres of different radii permitted to observe a significant size effect. Brittle mode consisting of surface ring cracks were observed at large scale (macroscopic scale) while localized plastic deformation with microcracks randomly distributed was observed at small scale (mesoscopic scale). Transmission electron microscopy observations of thin foils machined by ion milling were performed to investigate the subsurface damage. Numerical simulations with a code developed internally in LaMCoS laboratory enabled to follow the evolution of the plastic zone under pure rolling conditions. In these simulations, the nonlinear behaviour of ceramics was modelled using a bilinear law where Sy is the yield stress and K a hardening parameter of the ceramic specimen. Instrumented indentation tests were performed using a diamond spherical tip of radius 42 µm. Experimental load versus displacement curves were used as input data for an inverse identification purpose. Levemberg-Marquart algorithm was used to minimize the gap in the least squares sense
Porubský, Tomáš. "Studium vztahu mezi podmínkami testu FNCT (Full Notched Creep) a rychlostí šíření trhliny SCG (Slow Crack Growth) pro hodnocení odolnosti HDPE vůči růstu trhlin." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2015. http://www.nusl.cz/ntk/nusl-217107.
Повний текст джерелаMeriaux, Jean. "Etude expérimentale et modélisation de l'endommagement du contact aube-disque de soufflante soumis à des chargements de fretting fatigue." Phd thesis, Ecole Centrale de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00730679.
Повний текст джерелаBonniot, Thomas. "Fatigue crack growth under non-proportional mixed-mode loading in rail steel : From experiment to simulation." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX096/document.
Повний текст джерелаRails are submitted to Rolling Contact Fatigue due to repeated passages of train wheels, which induces several types of cracks, such as Squat-type cracks. Those cracks undergo non-proportional mixed-mode I + II + III loading, including compression phases, in variable proportions along the crack front, making the prediction of their paths and growth rates a challenge.Mode I crack growth kinetics, for positive and negative R ratios, were first determined in R260 steel, as well as friction-corrected crack growth kinetics for fully-reversed combined mode II and III. The effective Stress Intensity Factors (SIFs) were deduced from the measured in-plane and out-of-plane crack face sliding displacements. From those kinetic laws, it was deduced that neither pure mode I, nor pure shear mode loadings can explain the crack growth rates observed in rails. A combination of those three loading modes, according to complex loading paths had thus to be prospected.Non-proportional mixed-mode I + II fatigue crack growth tests were then performed, following representative loading paths. Stereo digital image correlation was used to measure the near-tip displacement field. Post-treatment methods generally used to deduce the effective SIFs from these fields were inappropriate because of contact and friction stresses along the crack face. New methods were thus developed. The crack paths and growth rates were analyzed, using the effective SIFs. Crack path prediction by the maximum tangential stress criterion was found not to be very reliable, but substantially improved when crack tip plasticity and the presence of contact and friction stresses along the crack faces were taken into account. The measured crack growth rates correlated well with a combination of the three effective SIFs in a Paris-type law.From these experiments, it appears that due to crack face roughness, asperities interlocking and friction substantially reduce the effective SIFs, even without any normal compression, which cannot be captured by a simple Coulomb’s law. Besides, crack faces wear also has a large influence on the effective SIFs. The challenge for structural applications is thus not only to choose the most appropriate bifurcation criterion and crack growth law, but also to take crack face roughness and wear into account, in order to estimate the correct effective SIFS to use in these models.For industrial applications, a simple engineering approach was proposed to integrate roughness-induced friction in the estimation of the effective loading path from the nominal one. This approach was validated on sequential mixed-mode I + II & III experiments
Simon, Samuel. "De la dynamique ferroviaire à l’accommodation microstructurale du rail : Contribution des TTS à la réponse tribologique des aciers : Cas du défaut de squat." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0028/document.
Повний текст джерелаSquats have recently become recognised as one of the major rolling contact fatigue defects in modern railway networks for which there is currently no solution other than preventive grinding operations or costly rail renewal. To better understand the entire damage mechanism of squat, A tribological and metallurgical analysis of the rolling band and the near surface layer was performed close to an incipient squat. This characterization show a significant anisotropy of the rail surface layer associated with developments of Tribological Transformation of Surface. These results reflect some specific wheel/rail contact conditions in this squat area, including an unusual level of shear forces in a straight track. In order to validate this observations, two tests were performed. On the one hand, the contact conditions in a squat area were measured from an instrumented train. On the other hand, the tribological response of the rail steel was studied through regular monitoring of a test site subjected to railway traffic. These tests allow to identify a high imbalance of the traction forces and the presence of local slips at the wheel/rail interface. Several thermomechanical initiation mechanism of squats are then given in a overall diagram of the tribological response of rail steels
German, Roman. "Vliv zbytkových napětí na kontaktní porušování keramických laminátů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-382550.
Повний текст джерелаPannemaecker, Alix de. "Etude du phénomène d'arrêt de propagation des fissures au travers d'un couplage multi-échelles fretting, fretting fatigue et essai fatigue C(T)." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0010/document.
Повний текст джерелаAircraft structures such as blade/disk, rivet/sheet and fretted or bolted assembly contacts are subjected to fatigue fretting damage caused by vibratory loads. These loads combining fretting (alternating micro displacements) and fatigue contact loading can induce cracks. The objective of this thesis is to identify the propagation and crack arrest mechanisms for different configurations involving fretting and fatigue loads. Various aspects will be studied : - Simple fretting, fatigue fretting and fatigue tests will be correlated in a way to measure some material mechanical properties. A reverse approach allowing to identify the long and short fatigue crack propagation thresholds from simple fretting and fretting fatigue will be introduced. - A new closure model taking into account the effect of loading ratio on crack closure in fretting and fretting fatigue tests will be proposed. - The scaling effect will be studied thanks to the development of a new fretting fatigue machine allowing for in-situ monitoring of the propagation of small scale cracks. The behavior of fretting short cracks has been observed for the first time in a fretting fatigue test. The main idea behind the current work is the consideration that for a simple fretting test, the crack will always lead to a crack propagation arrest condition. Threshold stress intensity factors can thus be extracted from fretting tests using a reverse method. The methodology used consists in measuring the longest fretting crack corresponding to a crack propagation arrest condition. Short and long crack regimes are studied by varying fretting loads and geometries. The corresponding threshold stress intensity factor is calculated for each arrest condition. A complete description of fatigue crack arrest thresholds can be obtained from a plot depicting the evolution of the stress intensity factor range as a function of crack length. This methodology has been applied on multiple simple fretting configurations and was extended to fretting fatigue tests allowing to study a large range of loading ratios. Conventional fatigue crack propagation tests were carried out on C(T) specimens in order to validate the reverse method used for crack arrest conditions. The present thesis is divided into six main chapters. Chapter 1 provides a complete literature review on short and long crack propagation in metallic materials introducing crack closure. It provides a treatment for both fretting and fretting fatigue including a comparative analysis. Chapter 2 provides an overview of the different techniques and methodologies used as part of this research project. The reverse method used for the identification of crack propagation arrest conditions as well as a numerical analysis are presented in Chapter 3. The following Chapters provide a treatment of the various results obtained. Chapter 4 focuses on simple fretting tests carried out on different metallic materials. A correlation between simple fretting and long fatigue crack arrest conditions was obtained for negative loading ratios. This analysis is extended to positive loading ratios in Chapter 5 combining simple fretting, prestressed fretting and C(T) fatigue tests. Finally, scaling effects and fretting fatigue crack propagation kinetics are studied in Chapter 6
Balcombe, Robbie. "A study of rolling contact fatigue cracks in lubricated contacts." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9848.
Повний текст джерелаLama, Salomon Abraham. "Digital State Models for Infrastructure Condition Assessment and Structural Testing." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/84502.
Повний текст джерелаPh. D.
Bossy, Etienne. "Influence des caractéristiques de microstructures nitrurées sur l’initiation d’écaillage en surface par fatigue de contact." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI095.
Повний текст джерелаEnergy performance enhancement in the transport industry leads manufacturers to lighten their systems. As a result, the contacting parts are more and more stressed. Where cracks were previously initiated on inclusions in sub-surface, more and more surface defects appear. In order to guarantee and improve the performance of the parts under rolling contact fatigue, gas nitriding treatment is widely used. This thermochemical treatment enhances the steel surface properties by introducing residual stresses and increasing its hardness. Although this treatment is widely studied, crack initiation phenomenon are still grey areas. Nitrided steels present a network of intergranular precipitations of cementite that are significantly harder than steel. Their role has been highlighted in the case of crack propagation but their role in initiation remains hypothetical. In addition, in some cases, surface defects coexist with subsurface fatigue. The model and experiments presented in this study provide answers on these issues. The fatigue behavior is modeled using a finite element model coupled with Dang Van fatigue criterion. The modelization of nitrided steel, and particularly of its material properties, is complex. Given the property gradient between the surface and the bulk material, the resistance limits are indeed different. Independently tested, it is shown that neither surface nor bulk parameters can correctly model the fatigue behavior of the whole material. It is necessary to take into account the property gradient to model a fatigue response corresponding to the experimental observations. In this study the gradient of fatigue properties, difficult to measure, is similar to the micro-yield stress, more accessible. This model highlight the reason for the coexistence of surface defects and subsurface fatigue in the studied case. Indeed, although the load is highly located on the surface, the decrease of property material in the subsurface causes the appearance of deep areas undergoing fatigue. Realized experiments highlight the role of cementite precipitates on initiation of cracks. Their over-presence near microcracks confirms indeed their disruptive role of the involved phenomena. These carbide boundaries, which elastic behavior is similar to that of steel, seem to speed up the initiation. This is explained by the incompatibility of deformations in the microplastic field around precipitates. This incompatibility causes the de-cohesion of these elements thus generating microcracks. These microcracks can cross the cementite precipitates, circumvent it or more rarely propagate in steel. In the end, the proposed model predicts the fatigue response behavior of nitrided steel. The hypotheses formulated on the role of carbide precipitation in the literature seem to be verified experimentally and allow to propose scenarios proposed based on experimental observations and realists physical considerations
Ciccarone, Charles. "Utilisation d'ondes de surface à l'aide de scanners acoustiques sans contact pour le contrôle non destructif de structures en béton." Thesis, Ecole centrale de Lille, 2020. http://www.theses.fr/2020ECLI0014.
Повний текст джерелаThis work proposes a method for the non-destructive testing of concrete for civil engineering structures.This method is based on the emission and reception - when the surface wave has passed through the material - ofacoustic sonic and ultrasonic waves. The waves used in this thesis are surface waves, as they have the property ofpenetrating the material to a depth equal to their wavelength. The auscultation of concrete is done using twoscanners: a first scanner applying this method with high frequency waves was used to characterize the concreteskin, while a second scanner using low frequency waves, developed within the framework of this work, made itpossible to characterize a concrete over the thickness of an entire wall. In order to determine the capabilities andlimitations of this method for the non-destructive testing of concrete, several pathologies or environmentalconditions of concrete were simulated in the laboratory on test specimens. These specimens were then examinednon-destructively with acoustic scanners and destructively with material tests. The pathologies or conditions inquestion were leaching, delamination, micro/macrocracking of the concrete, and its state of saturation. Comparisonof the results allowed us to conclude that this method and these scanners are able to detect and determine the depthof a leaching of concrete, as well as for a delamination within concrete, to follow the evolution of a saturation frontwithin a limestone but not yet within a concrete, and to detect and follow the stress and micro-cracking as well asthe evolution of macro-cracks, in particular thanks to automated measurements carried out in situ on the VeRCoRsstructure
Ciccarone, Charles. "Utilisation d'ondes de surface à l'aide de scanners acoustiques sans contact pour le contrôle non destructif de structures en béton." Thesis, Centrale Lille Institut, 2020. http://www.theses.fr/2020CLIL0014.
Повний текст джерелаThis work proposes a method for the non-destructive testing of concrete for civil engineering structures.This method is based on the emission and reception - when the surface wave has passed through the material - ofacoustic sonic and ultrasonic waves. The waves used in this thesis are surface waves, as they have the property ofpenetrating the material to a depth equal to their wavelength. The auscultation of concrete is done using twoscanners: a first scanner applying this method with high frequency waves was used to characterize the concreteskin, while a second scanner using low frequency waves, developed within the framework of this work, made itpossible to characterize a concrete over the thickness of an entire wall. In order to determine the capabilities andlimitations of this method for the non-destructive testing of concrete, several pathologies or environmentalconditions of concrete were simulated in the laboratory on test specimens. These specimens were then examinednon-destructively with acoustic scanners and destructively with material tests. The pathologies or conditions inquestion were leaching, delamination, micro/macrocracking of the concrete, and its state of saturation. Comparisonof the results allowed us to conclude that this method and these scanners are able to detect and determine the depthof a leaching of concrete, as well as for a delamination within concrete, to follow the evolution of a saturation frontwithin a limestone but not yet within a concrete, and to detect and follow the stress and micro-cracking as well asthe evolution of macro-cracks, in particular thanks to automated measurements carried out in situ on the VeRCoRsstructure
Ferré, Romain. "Etude expérimentale et modélisation de la durabilité d'un contact représentatif de l'interface aube / disque de soufflante grenaillé soumis à des chargements de fretting / fatigue / usure." Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0012.
Повний текст джерелаThis work aims at studying the crack initiation risk of a blade/disk contact under fretting/fatigue loading. The fan stage of a civil engine is studied and the material used is a titanium alloy: Ti-6Al-4V. This complex issue concerns small contacts which are subjected to high contact pressures and micro-displacements. Thus, a complex multiaxial loading occurs on the structure. Fretting, static stressed fretting and fretting fatigue testing are performed in order to quantify the crack nucleation thresholds. In addition, several geometries which present different stress gradient values are used. The experimental results show a stress gradient effect on the crack initiation. Thus, using a wide range of stress gradient, it has been confirmed that stress gradient delays crack nucleation. A multiaxial fatigue criterion is used to determine the equivalent stress field under the contact. Then, a non-local approach, identified thanks to one fretting experimental condition, is employed in order to consider the stress gradient effect. This approach provides the prediction of the whole experimental results. In this way, a predictive method of the initiation fatigue life has been introduced. This numerical approach takes into account the multiaxial loading, the stress gradient effect, the plastic-elastic behavior of the interface and the fatigue strength limits of the material. The blade/disk contacts of the engine are shot-peened. During the flight, interfaces are subjected to low displacement amplitudes leading to crack initiation. On the other hand, during landing and take-off, contacts are submitted to high displacement amplitudes leading to the interface wear. As a consequence, competition between wear kinetic and nucleation one is studied and “bell curves” are plotted (i.e. fatigue life time versus displacement amplitude).Moreover, the effect of the shot-peening residual stresses on fatigue life time is observed. In case of un-treated material, a beneficial impact on the fatigue life time is observed due to wear process. Compressive residual stresses of shot-peening increase the fatigue life when fretting/fatigue on partial slip regime occurs. Nevertheless, a decrease of the fatigue life time is observed when wear process is activated by the gross slip condition. Finally, the complex loading of the engine blade/disk contact has been reproduced in the laboratory. To achieve this, a new testing, using an experimental machine composed of three hydraulic actuators is developed. Thus, the global life time of the representative interface of the fan stage is studied. Oligocyclic (low frequency) and polycyclic (high frequency) solicitations interact themselves and lead, firstly, to a rearrangement of the residual stresses, and secondly, to an increase of the wear kinetics. This research work highlights the interest to consider the polycyclic loadings to design the blade/disk structure. These solicitations reproduce the “cracking” fatigue phenomenon, the cumulative damages and the wear kinetics of the interface
Le, Marion. "Influence des liserés de carbures induits par la nitruration gazeuse sur les mécanismes de fissuration de fatigue de contacts roulants." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0102/document.
Повний текст джерелаGas nitriding is a thermochemical surface treatment widely used by gear manufacturers to improve the rolling contact fatigue endurance of their components. Indeed, increasing the hardness and introducing compressive residual stresses to the geartooth surfaces inhibit or delay crack initiation and propagation. However, most of the alloyed steel nitrided layers show the presence of intergranular carbide networks. The precipitation of these carbides specifically occurs at parallel grain boundaries during the treatment and, being a carbon-rich phase, they are associated to tough and fragile heterogeneities. Besides, standards for gear material quality recommend a broad range of steel grain sizes which lead to various possible microstructures on gear components after nitriding. Indeed, the intergranular carbide network morphology depends on the steel grain size. Since there is no evidence regarding the real effect of the carbides on rolling contact fatigue, this work presents experimental investigations carried out on a twin-disc machine. The tests consist in reproducing surface-initiated pitting on specimens whose nitrided layers, obtained by a unique thermochemical surface treatment, display similar mechanical properties (hardness and compressive residual stresses) but different microstructures (grain sizes and carbide network morphologies). The first analysis resulted in suggesting the micro-crack nucleation mechanisms. In this study, the test conditions were chosen to induce these micro-cracks near the disc surfaces. For a given contact stress field, nucleation sites depend on the steel grain size and can take place at intergranular carbides. Investigations of crack networks led on cross sections and 3D observations by means of high energy X-ray computed tomography, coupled with compressive residual stress evolution analysis, help the authors proposing the rolling contact fatigue crack propagation scenarios in nitrided layers. When contact shear stresses locally exceed the material micro-yield shear stress limit, micro-deformations arise and add compressive residual stresses to the treated layers. To accommodate these volume variations the compressive residual stresses, initially induced by nitriding, release at depths where contact stresses are lower. The pre-existing residual stresses being less compressive, micro-cracks near the surface can propagate through the carbides that act as preferential crack growth sites. When the nitrided layers display high carbide density, the intergranular precipitates drag the cracks toward the core, whereas rolling contact fatigue failures are limited to the near surface when the distance between the precipitates is too important. Finally, the length and the continuity of the carbides, linked to the steel grain size, locally increase the crack propagation speed. This gives rise to a lower endurance to surface-initiated pitting in coarse microstructures
Mai, Si Hai. "Etude de dégradation des voies ferrées urbaines." Phd thesis, Université Paris-Est, 2011. http://pastel.archives-ouvertes.fr/pastel-00659068.
Повний текст джерелаDahlberg, Johan. "A numerical and experimental investigation on surface and sub-surface initiation of contact fatigue cracks at cylindrical contacts /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3887.
Повний текст джерелаGussmann, Pascal. "The small-deformation limit in elasticity and elastoplasticity in the presence of cracks." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19242.
Повний текст джерелаThe small-deformation limit in presence of a given crack is considered in three distinct continuummechanical models. First, a purely static finite-strain elasticity model is considered in the limit of small loading, where the constraint of global injectivity is shown to converge in the sense of Gamma-convergence to a local constraint of non-interpenetration along the crack. Second, finitestrain deformation plasticity based on the multiplicative decomposition of the strain tensor is shown to Gamma-converge to linearized deformation elastoplasticity with crack conditions. Third, the rate-independent evolution of elastoplasticity is considered with a generalized class of global injectivity constraints for the finite-strain model. On the one hand, neglecting the constraints the evolutionary Gamma-converge to linearized elastoplasticity is proven. On the other hand, a conjecture is made, subject to which the evolutionary Gamma-convergence with constraints still holds.
Яким, Р. С. "Науково-прикладні засади підвищення довговічності тришарошкових бурових доліт". Thesis, Івано-Франківський національний технічний університет нафти і газу, 2012. http://elar.nung.edu.ua/handle/123456789/1871.
Повний текст джерелаThe thesis is devoted to the problem connected with the durability increase of three-cone rock bits at all manufacturing stages. Much attention is paid to the durability and efficiency increase of V, VU, AU, bearing components, arm pins, cones, and insert rock-destroying equipment, and to the protection of rock bits against wear-and-tear across diameter. On the basis of complex experimental tests some propositions were determined. These propositions got practical application in domestic rock bit construction. Complex trend on the durability increase of rock bits is worked out on the ground of developed stepwise and logical analysis, which helps to establish the most authentic reason of rock bit failure. This trend includes the solving of problems connected with finding out of optimum physicomechanical properties, crack-resistance, hardness, contact endurance of used materials of components and their strengthening in accordance with operation standards; construction improvement of rock bits parts and units according to operation standards; qualitative solving of design and technological problems connected with design, engineering and manufacturing of rock bits and their parts. With this aim it is determined and tested criteria, some new methods and constructions protected by patents, and also measures directed at increase of qualitative realization of processes, which effectively prolong the rock bit parts durability at all stages of their manufacturing. Owing to theoretical and experimental investigations the search-engineering problems of three-cone rock bits durability increase are solved in a new way. At means that it is necessary to base on the results of complex search-engineering problems solving at all stages of rock bits life cycle. At allows to solve complex of design and technological problems connected with manufacturing and mobile mastering of new competitive constructions and standard sizes of rock bits relying on the unifed process approach.
Sun, Lingtao. "Etude numérique de l'amorçage et de la propagation de fissures de fretting." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00755695.
Повний текст джерелаSuhett, Helmer Gisèle. "Crack propagation on rock mass on the CO2 storage context." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1190/document.
Повний текст джерелаThe capture and the storage of CO2 (CSC) on the underground geological formations is a solution for the CO2 undesirable effects reduction. The geological formations being composed by heterogenic material have a crack network. The fracture toughness (KC) is a rock parameter connected with the capacity of a material to resist crack propagation. The propagation of a crack can be due to the changing of the stress or to the rock degradation. The evaluation of the fracture toughness and its evolution due to the chemical effects is then important to the modelling of the crack propagations on the CO2 storage context. One objective of this work is the experimental evaluation of the CO2 degradation on the fracture toughness. For the experimental program a preliminary study was made to the choice of the rock and the test to be performed. In this way, a limestone (Pierre de Lens) was chosen to be studied in an intact and degraded state. The degradation takes place in an autoclave, where the samples are put at CO2-saturated water in reservoir conditions (60 °C and 15 MPa).Several experimental tests are chosen for the evaluation of the fracture toughness in modes I and II. Some examples are the Central crack Brazilian disc (CCBD) for the mode I and the Punch through shear test (PTST) for the mode II. Some tests where performed using an image correlation technique (DIC). This set-up allows the fracture toughness evaluation by the displacement field evolution. The experimental results shows the fracture toughness values obtained by the different configurations are in good agreement. After the DIC technique analysis we can point the fracture toughness in mode II can not be evaluated in a non confined test. For the degradation process, the complementary analysis in the mercury porosimeter shows the rock porosity changing is low (0.4 %). At the SEM, the degradation can be observed by a homogenization of the sample. For the fracture toughness it value passes from 0.62 to 0.58 MPa.m0.5. We also have studied the effect of water performing tests in a saturated environment. The influence is more significant with a reduction on 17 % in the fracture toughness. The CO2 presence in the fluid does not affect this value. Concerning the mode II evaluation by the PTST test, the samples were submitted to different confining pressures (5, 10 and 15 MPa). We can observe a good evaluation of the fracture toughness in mode II (around 3 MPa.m0.5). Nevertheless, the mode II is still present for the pressures 5 and 10 MPa, and it is not inexistent for a 15 MPa pressure. Still in this case the influence of CO2 is low with values passing from 2.96 to 2.77 MPa.m0.5.The influence if the rock degradation by the CO2 presence on the crack propagation were studied by the help of a numerical model ENDO-HETEROGENE, that is present in the Code-Aster® calculation code. This model is base on the initiation and propagation of cracks in a heterogenic environmental where the parameter variability follows the 2 parameters Weibull probabilistic model (m and σ0). We exploited the possibility of the chemical degradation influence on the microstructure heterogeneity that is represented by the parameter m. The model shows that the changing of m influence on the crack number and dimensions by the maximum size of the crack didn't change. Putting this result in context, the Weibull parameters were evaluated for the intact and degraded rock. We observed that m changes from 8.55 to 8.52 and σ0 from 2.8 to 2.2 MPa. The numerical simulations show this variation is not enough to change the crack network that is formed after a load in a geological layer. The general results show that for a limestone reservoir the CO2 injection affect significantly neither the fracture toughness nor the probabilistic parameters. These results correspond to a 10 years period for a zone far from the injection point
Panico, Pierre. "Prévision de l'amorçage de fissures de fretting par une méthode asymptotique appliquée aux rotors d'hélicoptères." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI135.
Повний текст джерелаThe fretting damage phenomenon takes place in loaded mechanical contact interfaces subject to oscillatory small displacement and could lead to cracks nucleation. The prediction of such events is a major challenge for aeronautical industry. The length scale difference between industrial models and the local stress reveals some difficulties in the risk evaluation. An experimental campaign on a wide geometrical contacting pad range has been performed. Those fatigue tests involving fretting solicitation have been used to characterize the fretting crack nucleation at 1 million cycles with various geometries and loading. A correlation between the crack nucleation results and the material properties become possible by using asymptotic parameters. They are defined as the contact edge eigenvalues and are related to the shear stress and normal stress intensity. A fretting crack nucleation criterion is proposed taking advantage of the equivalence of the asymptotic description with contact mechanics and linear elastic fracture mechanics. A numerical method is finally developed to apply this fretting criterion on finite element industrial models. The numerical tool, or analytical patch, is working as a post-processing method based on analytical stress enrichment to minimize the mesh size dependence. This analytical patch is computing the contact edge asymptotic parameters at each time step. The application of the fretting crack nucleation criterion allows a fast and robust fretting crack risk evaluation on industrial parts
Bellecave, Johan. "Stress Gradients In Fretting Fatigue." Thesis, Cachan, Ecole normale supérieure, 2015. http://www.theses.fr/2015DENS0036/document.
Повний текст джерелаThis thesis is part of an international research program (IRG Cognac) initiated by the engine manufacturer SNECMA (SAFRAN group) involving ENS Cachan, UnB, ENSMA, CNRS, Snecma, Turbomeca et Messier Bugatti Dowty. The thesis focuses on the effect of a stress gradient in fretting fatigue. Fretting-fatigue refers to the damage process localized at the frontier of the contact between two contacting bodies subjected to fatigue loadings. The prediction of this phenomenon is of major importance in determining, for instance, the lifetime of fan's disc. In the vicinity of the contact front, the stress field inherited from the contact loads is maximal at the surface and displays a strong gradient from the surface. It was shown in this thesis, for a Ti-6AL-4V alloy, that local approaches, based on local stresses at the most critical point, are not appropriate to predict fretting fatigue lives. As a matter of fact, short cracks initiated at the most critical point may stop if the stress decay from the surface is strong enough or may continue their growth, up to the failure of the component, if the stress gradient from the surface is not string enough. A second difficulty is the multiaxial and non-proportional nature of the loading conditions. Fatigue-fretting stems from the combination of loads that have neither the same spatial distribution nor the same time-dependency. In fretting-fatigue tests, three loading components are considered, the fatigue loading of the component (cyclic), the normal part (assumed to be constant) and the in-plane part (cyclic) of the loads between the two contacting components. To quantify the effect of the stress gradient, tests were carried out on a fatigue testing contact bench developed at the University of Brasilia, with experimental conditions ensuring different stress gradient while keeping the maximal stress the same. Damage mechanisms were studied using post-mortem analysis and optical microscopy on the contact elements tested. The prediction of the fretting fatigue life was done using different approaches. The first one is based on the Critical Distance Method and a fatigue criterion. The second is based on a K-based short crack arrest method. Finally, a new criterion was proposed. This method considers a generalized von Mises yield criterion for the crack tip region and accounts for the T-stresses in the asymptotic LEFM development
Rycerz, Pawel. "Propagation of surface initiated rolling contact fatigue cracks in bearing steel." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44525.
Повний текст джерелаBriggs, Daniel. "The social context of crack using careers : an ethnographic study in London." Thesis, London School of Hygiene and Tropical Medicine (University of London), 2011. http://researchonline.lshtm.ac.uk/768501/.
Повний текст джерелаWretborn, Joel. "Modelling cracks in solid materials using the Material Point Method." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-136797.
Повний текст джерелаIssa, Ahmed Ali. "The influence of stone content and particle grading on strength characteristics for compacted soil." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340681.
Повний текст джерелаBower, A. F. "Some aspects of plastic flow, residual stress and fatigue cracks due to rolling and sliding contact." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382514.
Повний текст джерелаNikas, Georgios. "Theoretical modelling of the entrainment and thermomechanical effects of contamination particles in elastohydrodynamic contacts." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314006.
Повний текст джерелаPape, Anthony P. "Overdose: Constructing Television from the Cracks in the Superhero Content Conglomerate." Ohio University Honors Tutorial College / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors162025124846866.
Повний текст джерелаZhao, Ping. "Three-dimensional boundary element and experimental analysis of lubricant ceramic surface ring cracks in rolling contact." Thesis, Bournemouth University, 2006. http://eprints.bournemouth.ac.uk/10552/.
Повний текст джерелаShen, Jialong. "Responses of alternating current field measurement (ACFM) to rolling contact fatigue (RCF) cracks in railway rails." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/93593/.
Повний текст джерелаDahlberg, Johan. "On the asperity point load mechanism for rolling contact fatigue." Doctoral thesis, Stockholm : Hållfasthetslära, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4569.
Повний текст джерелаSteckenrider, John J. "Multi-Bayesian Approach to Stochastic Feature Recognition in the Context of Road Crack Detection and Classification." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/81752.
Повний текст джерелаMaster of Science
Humans have an outstanding ability to understand things about the world around them. We learn from our youngest years how to make sense of things and perceive our environment even when it is not easy. To do this, we inherently think in terms of probabilities, updating our belief as we gain new information. The methods introduced here allow an autonomous system to think similarly, by applying a fairly common probabilistic technique to the task of perception and classification. In particular, road cracks are observed and classified using these methods, in order to develop an autonomous road condition monitoring system. The results of this research are promising; cracks are identified and correctly categorized with 92% accuracy, and the additional “intelligence” of the system leads to a 33% improvement in road crack assessment. These methods could be applied in a variety of contexts as the leading edge of robotics research seeks to develop more robust and human-like ways of perceiving the world.
Vallim, Danielle de Carvalho. "Os passos indesejáveis: um estudo do contexto sociocultural do uso e usuários de crack nas cidades do Rio de Janeiro e Nova Iorque." Universidade do Estado do Rio de Janeiro, 2015. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=9200.
Повний текст джерелаA presente tese desenvolveu um olhar sobre o indivíduo que consome crack abusivamente nas cidades do Rio de Janeiro e Nova Iorque, especialmente os que se encontravam em situação de vulnerabilidade social. Neste sentido, buscou-se conhecer de que forma o processo de vulnerabilidade social corroborou para o uso abusivo da droga, concentrando, principalmente, o foco sobre os que se encontravam em condição marginal, especialmente aqueles que viviam em situação de rua, residindo nas cenas de uso. Rio de Janeiro e Nova Iorque foram escolhidas por apresentarem população usuária abusiva de crack em número considerável. Por isso, pretendeu-se analisar se os perfis socioculturais desses sujeitos se assemelhariam. Foram analisados significados complexos e conotações socioculturais que exerciam influências significativas nas motivações ao consumo abusivo da droga. Sendo assim, nas páginas que seguem, objetiva-se aprofundar a compreensão sobre os fenômenos sociais que interagem com ou sobre o uso abusivo de crack e com seus usuários, tendo como base o respeito aos indivíduos investigados. O processo de elaboração da pesquisa desenvolveu-se por meio da técnica de observação participante, história de vida e aplicação de entrevistas semi-estruturadas a usuários desta droga em ambas as cidades. Tanto no Rio de Janeiro, quanto em Nova Iorque, o perfil sociocultural dos participantes apresentou-se de forma semelhante: indivíduos socialmente marginalizados, excluídos, vítimas de racismo, preconceito, miséria, pobreza, conflitos familiares e rodeados pelos efeitos de políticas proibicionistas, assim como repressão policial e encarceramento. Pode-se afirmar que o processo de vulnerabilidade sofrido por esses indivíduos tornou-se evidente na vivência de problemas sociais anteriores ao consumo de crack. Estes problemas ampliaram-se na medida em que esses sujeitos se tornaram usuários abusivos, principalmente, frente ao estigma e à exclusão consequentes do fardo de serem drogados, cracudos ou crackheads, o que salientou ainda mais o rompimento dos vínculos sociais, na maioria dos casos, já enfraquecidos. Os resultados demonstraram que, embora sejam de cidades de diferentes países, com realidades econômicas, culturais e sociais distintas, a população usuária abusiva de crack se assemelha no que se refere aos aspectos especialmente as falhas - sociais, culturais e econômicas no processo de organização de vida, fortalecendo os argumentos em torno das dimensões socioculturais do uso.
This thesis is a investigation of the individual which consumes crack cocaine abusively at the cities of Rio de Janeiro and New York, especially those which were in social vulnerable situation. In this sense, was seen to know how the social vulnerability process corroborated to the abuse of drugs, focusing mainly on those who were marginalized, especially those living on the streets, at the spots of drug use. Rio de Janeiro and new york were chosen by the fact that there is a population of crack cocaine users in considerable numbers. Therefore, the aim was to analyze if the socio-cultural profiles of these subjects would resemble. Complex meanings and sociocultural connotations which exercised significant influence in the motivations of the abusive drug use were analyzed. Thus, in the pages that follow, the objective is to deepen the understanding of social phenomena that interact with or over the abusive use of crack cocaine and their users, based on respect for individuals investigated. The research process was developed through participant observation technique, life history and application of semi-structured interviews with crack cocaine users in both cities. Was discovered that both in Rio de Janeiro, as in new york, the socio-cultural profile of the participants were similar: socially marginalized people, excluded, victims of racism, prejudice, misery, poverty, family conflict and surrounded by the effects of prohibitionist policies and police repression and incarceration. It can be said that the vulnerability process of these individuals was presented in the life experience before to crack cocaine use. These problems have widened the extent that these subjects became abusive users, especially because the stigma and consequent exclusion of the "burden" of being , "cracudos" or "crackheads", which further emphasized the rupture of social links, in most cases, already weakened. The results show that, while the cities of different countries with economic, cultural and social realities different, the abusive users population of crack cocaine is similar with regard to the aspects - especially the failures - social, cultural and economic in the process of life organization, strengthening the arguments around the sociocultural dimensions of use.
Herbig, Michael. "3D short fatigue crack investigation in beta titanium alloys using phase and diffraction contrast tomography." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00690521.
Повний текст джерела